# tdd

A TDD rule guide for AI coding assistants that enforces the red-green-refactor workflow. Helps models write reliable unit tests before touching application code.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 424 installs · ★ 39
- Author: PyModel
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/PyModel/react-frontend-skills/tree/HEAD/skills/tdd/SKILL.md
- Updated: 2026-10-21
- HTML: https://affpapa.org/en/nevibecode/skills/pymodel-tdd

## What it does

The skill provides a structured guideline of 42 test-driven development rules grouped into 8 prioritized tiers. It forces the agent to follow the standard cycle: write a failing test, produce the minimum code necessary to pass, and clean up the result right away.

Every rule references a dedicated file under `references/<rule-id>.md` showing the underlying reason alongside bad versus good code patterns. The collection covers Arrange-Act-Assert structure, factory and builder patterns for data, external dependency stubs, and unit test execution speed without arbitrary sleep delays.

Framework-specific syntax for Vitest or network mocking with MSW is not part of this skill. PyModel delegates those topics to companion skills `vitest` and `msw`.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add PyModel/react-frontend-skills --skill tdd -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/tdd/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/tdd/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add PyModel/react-frontend-skills --skill tdd -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/tdd/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add PyModel/react-frontend-skills --skill tdd -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/tdd/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install PyModel/react-frontend-skills tdd
```

2. **Manually: put the files in place**
- File: `.github/skills/tdd/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add PyModel/react-frontend-skills --skill tdd -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/PyModel/react-frontend-skills --path skills/tdd
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/tdd/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add PyModel/react-frontend-skills --skill tdd -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/PyModel/react-frontend-skills/tree/HEAD/skills/tdd/SKILL.md

## When to use it
- enforce strict red-green-refactor steps in AI-generated code
- isolate unit tests from external dependencies and shared mutable state
- eliminate arbitrary sleep delays and flaky test logic
- organize test suites around user behavior instead of class methods

## Example prompts
- Implement this payment processor feature using TDD, starting with a failing test
- Review existing unit tests against the rule design-avoid-logic-in-tests
- Refactor the test fixtures using factories instead of shared global state

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 1c48c3e12a47710e.

BEGIN THIRD-PARTY FILE 1c48c3e12a47710e
```text
---
name: tdd
description: Test-driven development with red-green-refactor.
---

# Community Test-Driven Development Best Practices

Comprehensive guide to Test-Driven Development practices, designed for AI agents and LLMs. Contains 42 rules across 8 categories, prioritized by impact to guide test writing, refactoring, and code generation.

## When to Apply

Reference these guidelines when:
- Writing new tests using TDD workflow
- Implementing the red-green-refactor cycle
- Designing test structure and organization
- Creating test data and fixtures
- Reviewing or refactoring existing test suites

## TDD Workflow

1. **RED**: Write a failing test that defines desired behavior
2. **GREEN**: Write minimal code to make the test pass
3. **REFACTOR**: Clean up code while keeping tests green
4. Repeat for each new behavior

## Rule Categories by Priority

| Priority | Category | Impact | Prefix |
|----------|----------|--------|--------|
| 1 | Red-Green-Refactor Cycle | CRITICAL | `cycle-` |
| 2 | Test Design Principles | CRITICAL | `design-` |
| 3 | Test Isolation & Dependencies | HIGH | `isolate-` |
| 4 | Test Data Management | HIGH | `data-` |
| 5 | Assertions & Verification | MEDIUM | `assert-` |
| 6 | Test Organization & Structure | MEDIUM | `org-` |
| 7 | Test Performance & Reliability | MEDIUM | `perf-` |
| 8 | Test Pyramid & Strategy | LOW | `strat-` |

## Quick Reference

### 1. Red-Green-Refactor Cycle (CRITICAL)

- `cycle-write-test-first` - Write the Test Before the Implementation
- `cycle-minimal-code-to-pass` - Write Only Enough Code to Pass the Test
- `cycle-refactor-after-green` - Refactor Immediately After Green
- `cycle-verify-test-fails-first` - Verify the Test Fails Before Writing Code
- `cycle-small-increments` - Take Small Incremental Steps
- `cycle-maintain-test-list` - Maintain a Test List

### 2. Test Design Principles (CRITICAL)

- `design-test-behavior-not-implementation` - Test Behavior Not Implementation
- `design-one-assertion-per-test` - One Logical Assertion Per Test
- `design-descriptive-test-names` - Use Descriptive Test Names
- `design-aaa-pattern` - Follow the Arrange-Act-Assert Pattern
- `design-test-edge-cases` - Test Edge Cases and Boundaries
- `design-avoid-logic-in-tests` - Avoid Logic in Tests

### 3. Test Isolation & Dependencies (HIGH)

- `isolate-mock-external-dependencies` - Mock External Dependencies
- `isolate-no-shared-state` - Avoid Shared Mutable State Between Tests
- `isolate-deterministic-tests` - Write Deterministic Tests
- `isolate-prefer-stubs-over-mocks` - Prefer Stubs Over Mocks for Queries
- `isolate-use-dependency-injection` - Use Dependency Injection for Testability

### 4. Test Data Management (HIGH)

- `data-use-factories` - Use Factories for Test Data Creation
- `data-minimal-setup` - Keep Test Setup Minimal
- `data-avoid-mystery-guests` - Avoid Mystery Guests
- `data-unique-identifiers` - Use Unique Identifiers Per Test
- `data-builder-pattern` - Use Builder Pattern for Complex Objects

### 5. Assertions & Verification (MEDIUM)
```
END THIRD-PARTY FILE 1c48c3e12a47710e

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